Effect of La3+ on evolution of TiO2 coating layers on lamellar sericite and their pigmentary properties

TiO2-coated sericite powders were prepared by the chemical deposition method starting from lamellar sericite and TiCl4 in the presence of La3+. After calcination at 900 degrees C for 1 h, the resultant TiO2 nanoparticles on the sericite surfaces exist in anatase phase. The light scattering indexes of the TiO2-coated lamellar sericite powders are dozens of times higher than those of the naked lamellar sericite powders, varying with different contents of La3+. The presence of La3+ in the deposition solution is beneficial to the formation of the small-sized anatase TiO2 nanoparticles. The presence of La3+ also favors the formation of the dense and uniform island-like TiO2 coating layers in a large range of the mass ratio of TiO2 to sericite from 5% to 20%. XPS analysis shows that when La3+ is absent in the reaction solution, TiO2 coating layers anchor on the sericite surface via Ti-O-Si and Ti-O-Al bonds. The presence of La3+ causes the formation of Si-O-La and Al-O-La bonds on the sericite surface and Ti-O-La bond on the surface of TiO2 coating layers.